Humans have always discovered the laws governing nature through trial and observation. A falling apple is supposed to have given Newton the idea for his gravitational theory. Three hundred years later, international collaborations of hundreds of scientists are building highly precise measuring instruments to find evidence of the gravitational waves that Einstein later postulated. The LIGO Gravitational-Wave Observatory was able to prove this distortion in space and time last year in one of the most recent spectacular examples of the extremely high measurement accuracy of laser-based instruments. The tiny distortion in space has in the meantime been demonstrated between two mirrors in kilometer-long optical interferometers.
However, in doing so, researchers have had to deal with a persistent problem for many years. The accuracy of the optical resonators used are being limited by the quality of the mirrors. Measurement apparatuses have in the meantime become so accurate that even the thermal movement of the dielectric mirror coatings contaminate the signals. Dr. Garrett Cole, materials scientist from California, and Professor Markus Aspelmeyer of the University of Vienna have found a brilliant solution to this problem.
They followed a fundamentally new path and used the unique optical and mechanical properties of crystalline semiconductors to create novel, stable mirror coatings that reduce thermal noise by a factor of ten. They founded the company Crystalline Mirror Solutions in 2012. With its head office in Vienna and a production site in Santa Barbara in Silicon Valley, the company markets these crystalline mirrors for laser optics. Cole and Aspelmeyer have developed a process that makes it possible to transfer coating structures made of epitaxially produced monocrystalline semiconductors to arbitrary substrates, including those with a curved surface. Mirrors of this type can significantly further improve the sensitivity of future gravitational wave observatories or the accuracy of optical atomic clocks. These optical clocks already achieve relative accuracy, which can be used to observe relative changes in clock frequency through the Earth’s gravitational field by moving one of two clocks only a few centimeters higher.
However, the novel crystalline mirrors could also be used for interesting applications outside of basic research. With fifty times higher heat conduction than conventional mirror coatings, they offer a decided advantage. This property is of especially great interest for high-power laser applications, also in material processing. Moreover, the new technology is the first to make possible highly reflective mirrors with low optical losses in the mid-infrared spectral range, an area of growing importance. In this, molecular trace gases are detected by highly sensitive laser spectrometers in applications ranging from environmental protection to medical diagnostics.